The invention relates to a flat display device comprising a substantially evacuated envelope having mainly flat, substantially parallel front and rear walls, a layer of luminescent material along the inner surface of the front wall and at least one cathode unit having at least one cathode for generating at least one electron beam which moves substantially in a plane parallel to the front and rear walls via electron guns means, and which can be selectively deflected in the direction of the layer of luminescent material via deflection means in a vertical deflection unit, so that each beam scans at least a part of the layer of luminescent material.
The invention also relates to a cathode unit for use in a display device of the type described.
A display device of this type holds out the possibility of realizing thin flat television screens. Research is being done on constructions of such types to enable reduction in the thickness of the glass walls, while maintaining the strength necessary for the high vacuum. Other points of research aim at obtaining a uniform brightness throughout the picture surface, independent of the driven pixel, and the possibility of integration with control electronics.
A display device of the type described in the opening paragraph is known from Netherlands Patent Application No. 76,10521 laid open to public inspection.
In this device electron beams either from a source for one beam or from a line cathode arranged on or along the end wall of channels, respectively, are guided through the channels and subsequently they are not only deflected to the phosphor screen, but also are scanned in the transverse direction of the channel by means separate from the electron gun, to simplify the electron gun for such a device.
The dimensions of conventional cathodes are such that generated electron beams of two cathodes located at a minimum distance from each other enclose a plurality of pixel columns, thus requiring a horizontal deflection over a plurality of pixels. Moreover, the energy supplied is high. Thus, the solution proposed in the above-cited Patent Application is extremely costly on grounds of energy considerations and extra material costs (horizontal deflection electrodes in the channels).
The use of semiconductor cathodes in different display devices has already been proposed, notably in U.S. Pat. No. 4,303,930. However, such cathodes have the drawback that, although they amply meet the requirements imposed on dimensions for use in a device in accordance with NL 7610521, their efficiency rapidly deteriorates due to an ion bombardment caused by positive ions which are created notably in the high-voltage section of the device.